1. Field of the Invention
The present invention relates generally to a process for determining a remaining life of a component (or, part) suffering from erosion or oxidation due to operation of the component (or, part) under relatively high temperatures, and more specifically to a process for determining a remaining life of a gas turbine engine airfoil exposed to relatively high temperatures under normal operation of the component in which the component suffers from erosion or oxidation damage.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as an industrial gas turbine (IGT) or an aero gas turbine engine, stator vanes and shrouds, and rotor blades in the turbine section are exposed to an extremely high temperature gas flowing over the surface of these turbine components. In the forward or upstream stages of the turbine, the airfoils can be exposed to a gas flow temperature above the melting point of the metal alloy material. Without internal cooling, these airfoils could not be used under these conditions.
Turbine airfoils are typically made from superalloys with overlay or diffused coatings (TBC) which allow for high temperature exposure while offering high strength. One of the primary deterioration processes of a component occurs when superalloys and coatings react with oxygen that produce either or both sulfidation or high temperature oxidation or erosion damage to the base alloy or coatings. Sulfidation occurs at lower temperatures (below 1600 degrees F.) through damaging particulates found in the fuel burned to produce the hot gas flow. Sulfur contained in the fuel will produce a sulfur oxide buildup on the airfoil surface that—through time—will erode the surface of the airfoil or turbine component. Salts contained in the compressed air used to burn the fuel can also build up on the surface of the airfoil and will produce erosion.
Oxidation and erosion is the process when a second primary deterioration process of a component occurs from airfoils or components that are exposed to high temperatures (above 1600 degrees F.) which produce a depletion of the surface protecting alloy and coating elements, resulting in the coating and alloy surface oxidation and subsequent erosion. When the erosion on an airfoil or turbine component becomes too severe, the performance of the component can become significantly reduced, or the structural integrity of the airfoil can be impacted such that thermo-mechanical fatigue (TMF) cracks can occur on the component or the component breaks. Broken components passing through an engine can produce additional damage to the engine beyond that of the corrosion or erosion problems.
Corrosion can appear as a single location on a component in which the location can continuously erode until a hole appears in the component. If the component is an internally cooled airfoil, the resulting hole can allow for the cooling air to pass through the hole and out into the gas path. In some cases, this cooling air leakage could be critical to the performance of the airfoil or component and the engine.
Engine-run turbine airfoils or components are typically reused in an engine if the damage to the component is not too severe such that the component will last during the next cycle of engine operation. The determination of the remaining life of an eroded component based on the amount of alloy and coating loss which has occurred is critical to determining whether the component can continue in operation for a predetermined amount of time.